Apparatus for adjusting the relative positions of the cylinders in offset printing machines

ABSTRACT

The bearings of the offset cylinder are mounted in a pair of link mechanisms each made up of four pivotally connected links and arranged so that the offset cylinder can be adjusted to be in constant rolling engagement with the printing film cylinder and the impression cylinder and also so that the axis of the offset cylinder can be displaced around a circle whose centre lies on the line which passes through the axis of the offset cylinder and is parallel with the line connecting the axes of the printing film cylinder and the impression cylinder.

United States Patent [191 J iihme June 11, 1974 1 APPARATUS FOR ADJUSTING THE RELATIVE POSITIONS OF THE CYLINDERS IN OFFSET PRINTING Australia 101/185 1/1918 Great Britain 101/218 6/1927 Great Britain .1. 101/218 57 9 ABSTRACT The bearings of the offset cylinder are mounted in a pair of link mechanisms each made up of four pivotally connected links and arranged so that the offset cylinder can be adjusted to be in constant rolling engagement with the printing film cylinder and the impression cylinder and also so that the axis of the offset cylinder can be displaced around a circle whose centre lies on the line which passes through the axis of the offset cylinder and is parallel with the line connecting the axes of the printing film cylinder and the impression cylinder.

4 Claims, 2 Drawing Figures APPARATUS FOR ADJUSTING THE RELATIVE POSITIONS OF THE CYLINDERS IN OFFSET PRINTING MACHINES BACKGROUND OF THE INVENTION The present invention relates to an apparatus for adjusting the relative position of the offset cylinder with respect to the printing film cylinder and the impression cylinder in an offset printing or duplicating machine.

In order to even out any differences in thickness of the rubber cloth or of the printing films employed, it is necessary, at least in the case of larger machines in which stringent requirements are imposed as regards accuracy of register of the printed image, to adjust the cylinders i.e. to even out the thickness of the film or rubber cloth by means of underlays so that the intended cylinder circumferences are obtained. On account of the necessary correct development of the cylinders in relation to each other for obtaining property registered print's, particularly in multi-colour printing, the abovementioned difficult step has to be taken and this is not possible for newcomers to the art, because of their lack of experience.

To avoid an adjustment of this kind in the case of machines to be used in offices and the like, the only step taken so far has been that of prescribing the use of rubber cloths and printing films of very specific thickness matched to the required circumference of the cylinder in the case of small offset printing and duplicating machines, and particularly those not intended to be used exclusively by trained operators. This largely ensures correct development between the plate cylinder and the offset cylinder. The differences in the thickness of the paper to be printed upon can be dealt with by means of devices for altering the cylinder pressure and which vary the size of the gap between the rubber-cloth cylinder and the impression cylinder. This adjustment of the cylinders results in a good printed image, being applied to the sheet of paper since when the cylinders are too close together the image would be compressed whereas with the cylinders too far apart the image would not appear or would appear only in part.

Although the use of different thicknesses of rubber cloth and/or printing film results in a change in the cylinder-development conditions and therefore in the position of the printed image, it has been found in thecase of offset printing and duplicating machines in the sizerange here of interest, i.e. in the case of machines to be used in offices and the like, that such changes in position is not noticeable particularly in the case of monotone printing. Thus, in the case of such smaller machines intended only for monotone printing and for operation by personnel having no special technical knowledge, the possibility is likewise offered of optionally using different thicknesses of rubber cloth and printing film while ignoring the change in the cylinderdevelopment conditions, provided that it is possible to avoid spoiling the quality of print as occurs by compression of the image or by the absence of image at points corresponding to those where the film has an image, these defects resulting from the gap between the printing film and the rubber-cloth cylinders being too' small or too large.

Therefore, to allow for the differences in the thick nesses of film and/or rubber cloth, it is proposed to vary the distance between the film cylinder and the rubber cloth cylinder in order to obtain a correct printed image, the gap between the rubber cloth cylinder and the impression cylinder being set as previously. At the same time it must also be possible, if necessary and as in the past, to spread the three cylinders that roll over each other i.e. it is necessary to be able to bring the cylinders into positions in which there is a certain gap between them as required, for example, when fitting a new film or when the machine is at a standstill for a fairly lengthy period.

SUMMARY OF THE INVENTION The present invention seeks to provide a means for adjusting the cylinders of offset printing and duplicating machines whereby the distance between the printing film cylinder and the rubber cloth cylinder can be set without changing the distance between the impression cylinder and the rubber cloth cylinder, and the cylinders, rolling one over the other can, if required, also be moved away from each other.

According to the invention thre is provided an apparatus for adjusting the relative positions of the offset cylinder with respect to the printing film cylinder and the impression cylinder of an offset printing or duplicating machine, wherein the axis of the cylinders are mutually parallel. This apparatus comprises a bearing" for rotatably mounting a shaft on which the offset cylinder rotates, and means for permitting such bearing to be adjustably positioned at any point on a first circle whose centre lies on an extension of the straight line passing through the axis of the impression cylinder and that of the offset cylinder, and also for permitting such bearing to be moveable about a second circle whose centre lies on a straight line passing through the axis of the offset cylinder and parallel with the straight line connecting the axis of the printing film cylinder and that of the impression cylinder.

Preferably such means-comprises a four element link mechanism having a first link member which can be rotated into its setting position about an axis which lies on the extension of the first-mentioned straight line, a second link member swingably connected to the first link member at a point which lies on the second-mentioned straight line, and a third and fourth link member mutually swingably connected to the first and second link members to complete the link mechanism. The bearing is located at the point of swingable connection of the second and third link members, and the apparatus further comprises means for adjustably fixing the angle between the third and fourth link members to correspond to the angle at which the three cylinders roll over each other.

Such cylinder-adjusting means in the form of a special bearing for the shaft of the rubber-cloth cylinder is of course, provided atboth ends of that cylinder.

In a further embodiment the first link member is rotated into its setting position about such axis by means of an eccentric drive engaging this link member. Thus, by simply turning a wheel connected to the eccentric drive, the setting necessary for a particular thickness of printing film or rubber cloth can be carried out manually by reference to a scale.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be better understood two embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic view of an apparatus according to a first embodiment of the invention; and

FIG. 2 is a diagrammatic view of a modified embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a known arrangement of a printing film cylinder 6, rubber-cloth or offset cylinder and impression cylinder 7 in an offset printing or duplicating machines, the centres of the cylinders as seen in section, being located at the corners of a triangle.

The shaft 13 of the rubber-cloth cylinder 5 is mounted with the aid of the apparatus of the invention which takes the form of a four element link mechanism 2, 4, 10, 11 which can be displaced in its own plane, and one link can be locked in a particular position so that the link mechanism can be swung about a shaft as a rigid component.

The link mechanism comprises a first link member 2 which can be swung about a pivot pin 3 mounted in the frame of the machine. This swinging movement is indicated by the double-headed arrow 18 and may be achieved with the aid of an eccentric drive I which is connected to a setting wheel, not shown, on the exterior of the machine.

This one pivot pin 3 about which the link mechanism is swung in the rigid condition is so positioned that the bearing for the shaft 13 of the rubber-cloth cylinder 5 moves along a circle 14, of which the centre 3 lies approximately on a first straight line passing through the centre of the impression cylinder 7 and the centre of the rubber-cloth cylinder 5 when the latter cylinder rolls over the first, i.e. when the three cylinders occupy the nonnal position in relation to each other, as shown in the drawing. Since the adjustment of the cylinders, i.e. the swinging movement of the rigid link mechanism, uses only a very small portion of the circle, the rubber-cloth cylinder 5 mainly moves towards or away from the printing film cylinder 6 during this swinging movement without changing the distance from the impression cylinder 7.

The link mechanism also comprises a second link member 4 which is secured to the first link member 2 at 12. At the point of connection between the second link member 4 and the third link member 10 is mounted the shaft 13 of the rubber-cloth cylinder, whereas the third link member 10 is in turn connected to the first link member 2 by a fourth link member 11. To enable the link mechanism in the normal condition to behave as a rigid system, the angle between the link member 10 and 11 is fixed by linking a draw rod 9 (FIG. 2) to their connection 16, which draw rod extends substantially trasversely of the two link members and is secured against longitudinal displacement. The draw rod is secured by a latching device 17. Alternatively it can be connected to the manually operable cylinder control unit (not illustrated) which contains the latching device 17.

With the aid of the cylinder control unit, the apparatus can be so actuated that the rubber-cloth cylinder 5 moves away from the two other cylinders. For this pur- LII pose the latching device 17 is rendered inoperable, and pull is exerted on the draw rod 9 in the direction away from the link mechanism. The link mechanism is then no longer rigid and the link member 4 which swings about the pivot 12 is so positioned that, seen in the cross-sectional drawing it lies approximately on a second line which is parallel with a third line connecting the centre of the impression cylinder 7 and the centre of the printing film cylinder 6 and extends through the centre of the rubber-cloth cylinder 5 when the latter is in the normal position in which it is in contact with the two other cylinders.

This choice of the position of the pivot 12 results in shaft 13 of the rubber-cloth cylinder 5, upon separation of the cylinder, moving over a portion of the circle 15 that moves away from the two other cylinders, which portion can be regarded as being substantially straight in the zone utilized if the radius of the circle is sufficiently great.

By means of the arrangement described, the distance between the cylinder 5 and the cylinder 6 can be set when the draw rod 9 is secured, without the distance from the impression cylinder 7 being changed, whereas if necessary, by releasing draw rod 9, the rubber-cloth cylinder 5 can be moved away from the two other cylinders.

As already mentioned, cylinder adjusting means as described are provided at both ends of the shaft 13. An adjusting screw 8 illustrated in FIG. 2, upon which the eccentric drive 1, acts, serves the purpose of bringing the shaft l3v parallel with the two other cylinders.

I claim:

I 1. For use in a printing machine including, in combination, an offset cylinder, a printing film cylinder and an impression cylinder;

an apparatus for adjusting the relative position of the offset cylinder with respect to the printing film cylinder and the impression cylinder wherein each of saidcylinders have central longitudinal axes, said axes being mutually parallel, said apparatus comprising:

a shaft positioned at said axis of said offset cylinder, said offset cylinder being rotatably mounted thereon, and

means for mounting said shaft about a first pivot which defines a center of a first circle, said center lying on an extension of a first straight line passing through said axis of said impression cylinder and said axis of said offset cylinder,

means for mounting said shaft about a second pivot which defines a center of a second circle, said center lying on a second straight line passing through said axis of said ofiset cylinder, parallel with a third straight line connecting said axis of said printing film cylinder and said axis of said impression cylinder, and

means for selectively adjustably moving said shaft along said first circle for selectively moving said offset cylinder away from said printing cylinder while maintaining said ofi'set cylinder in contact with said impression cylinder, and for selectively adjustably moving saidshaft along said second circle for selectively moyingsaid offset cylinder simuitaneously away from both said'printing film cylinder and said impression cylinder.

2. An apparatus according to claim 1 wherein said means for mounting said shaft about a first pivot and said means for mounting said shaft about a second pivot comprises a four element link mechanism having a first link member mounted to rotate about an axis which lies on the extension of said first straight line, a second link member pivotally connected to the first link member at a point which lies on said second straight line, a third link member pivotally connected to said second link member, and a fourth link member pivotally connected to said third and first link members to complete said link mechanism, said shaft being located at the point of pivotable connection between said second and third link members, and said apparatus further comprising means for selectively adjustably fixing the angle between said third and fourth link members to correspond to the angle at which the three cylinders roll over each other and for thereby selectively ridigly fixing said link elements in an immovable position with respect to each other.

3. An apparatus according to claim 2, further comprising an eccentric drive means engaging said first member for rotating said first link member about its axis.

4. An apparatus according to claim 2, wherein said angle fixing means comprises a draw rod connected to the point of pivotal connection between said third and fourth link members, said draw rod extending substantially transversely of said'third and fourth link members, and means for securing said draw rod against longitudinal displacement, said securing means comprising a latching device to fix said third and fourth link members-in position so that they form with each other said angle corresponding to that at which said three cylinders roll over each other. 

1. For use in a printing machine including, in combination, an offset cylinder, a printing film cylinder and an impression cylinder; an apparatus for adjusting the relative position of the offset cylinder with respect to the printing film cylinder and the impression cylinder wherein each of said cylinders have central longitudinal axes, said axes being mutually parallel, said apparatus comprising: a shaft positioned at said axis of said offset cylinder, said offset cylinder being rotatably mounted thereon, and means for mounting said shaft about a first pivot which defines a center of a first circle, said center lying on an extension of a first straight line passing through said axis of said impression cylinder and said axis of said offset cylinder, means for mounting said shaft about a second pivot which defines a center of a second circle, said center lying on a second straight line passing through said axis of said offset cylinder, parallel with a third straight line connecting said axis of said printing film cylinder and said AXIS of said impression cylinder, and means for selectively adjustably moving said shaft along said first circle for selectively moving said offset cylinder away from said printing cylinder while maintaining said offset cylinder in contact with said impression cylinder, and for selectively adjustably moving said shaft along said second circle for selectively moving said offset cylinder simultaneously away from both said printing film cylinder and said impression cylinder.
 2. An apparatus according to claim 1 wherein said means for mounting said shaft about a first pivot and said means for mounting said shaft about a second pivot comprises a four element link mechanism having a first link member mounted to rotate about an axis which lies on the extension of said first straight line, a second link member pivotally connected to the first link member at a point which lies on said second straight line, a third link member pivotally connected to said second link member, and a fourth link member pivotally connected to said third and first link members to complete said link mechanism, said shaft being located at the point of pivotable connection between said second and third link members, and said apparatus further comprising means for selectively adjustably fixing the angle between said third and fourth link members to correspond to the angle at which the three cylinders roll over each other and for thereby selectively ridigly fixing said link elements in an immovable position with respect to each other.
 3. An apparatus according to claim 2, further comprising an eccentric drive means engaging said first member for rotating said first link member about its axis.
 4. An apparatus according to claim 2, wherein said angle fixing means comprises a draw rod connected to the point of pivotal connection between said third and fourth link members, said draw rod extending substantially transversely of said third and fourth link members, and means for securing said draw rod against longitudinal displacement, said securing means comprising a latching device to fix said third and fourth link members in position so that they form with each other said angle corresponding to that at which said three cylinders roll over each other. 